What's stiff-person syndrome?
Stiff-person syndrome is a rare autoimmune neurological disorder defined by progressive muscle rigidity (stiffness) and episodes of painful muscle spasms, typically in the trunk and limbs. Most people with the classic form carry antibodies against glutamic acid decarboxylase 65 (GAD65); a smaller subset is paraneoplastic, linked to an underlying cancer and to anti-amphiphysin antibodies.
| Also indexed as | ORPHA:3198, MONDO:0008491 |
|---|---|
| Features mapped | 12 |
| Treatments mapped | 6 |
| Published sources | 11 |
| Last reviewed | 2026-08-04 |
Signs and symptoms
Diabetes mellitus
In about 30 to 40% of people with stiff-person syndrome, the condition occurs alongside type 1 diabetes.
Autoimmune antibody positivity
In a cohort of people with stiff-person syndrome who were GAD65 antibody positive, about two thirds had at least one coexisting autoimmune disease.
Anti-GAD65 antibody
Most people with the classic form, roughly 80 percent, have antibodies against glutamic acid decarboxylase 65 (GAD65). These same antibodies also appear in other conditions such as type 1 diabetes and some forms of cerebellar ataxia, so the antibody is shared across disorders rather than unique to this one.
Anti-Amphiphysin antibody
In the paraneoplastic form, anti-amphiphysin antibodies are often present and point to an underlying cancer, such as breast cancer or small cell lung cancer.
Anti-GlyR antibody
Antibodies against the glycine receptor alpha 1 have been reported in about 12% of people with stiff-person syndrome.
Falls
The combination of muscle stiffness and spasms can cause sudden, uncontrolled falls, often without the normal reflexes that would break a fall.
Anxiety
Anxiety is closely linked to stiff-person syndrome and can trigger the muscle spasms, alongside specific phobias and startle. This is part of the condition itself, not a sign that the symptoms are imagined.
Exaggerated startle response
An exaggerated startle response is characteristic: a sudden noise or touch can trigger stiffening or a spasm.
Gait disturbance
Stiff-person syndrome spectrum disorders are characterized by fluctuating muscle stiffness, painful spasms, gait disturbance (difficulty walking), and hypersensitivity to triggers.
Rigidity
Stiff-person syndrome is characterized by muscle rigidity, along with sporadic muscle spasms and chronic muscle pain.
Intermittent painful muscle spasms
Stiff-person syndrome is characterized by axial muscle stiffness, rigidity, and intermittent painful muscle spasms. Axial means the muscles of the trunk and spine.
EMG abnormality
On electromyography, stiff-person syndrome characteristically shows continuous motor unit activity, meaning the muscles keep firing electrically even at rest.
How it is diagnosed
Stiff person spectrum disorder
Diagnosed using: anti-GAD65 antibody test.
“Almost 80% of patients with classic SPS harbor autoantibodies against glutamic acid decarboxylase 65 (GAD65).”
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
benzodiazepines
Benzodiazepines, which boost the calming neurotransmitter GABA, are a first-line option for easing the stiffness and spasms. They treat symptoms rather than the underlying autoimmune process; the paraneoplastic form also needs treatment of the underlying cancer.
Used to help with: Stiff person spectrum disorder.
“For treatment, we suggest starting with benzodiazepines as first-line treatment.”
Intravenous immunoglobulin (IVIG)
Intravenous immunoglobulin (IVIG) is an immune-based treatment used for stiff-person syndrome, particularly when symptoms do not respond well to first-line muscle relaxants. It is given as infusions.
Used to help with: Stiff person spectrum disorder.
“…intrathecal baclofen, intravenous immunoglobulin (IVIG), or…”
diazepam
Most people with stiff-person syndrome have sustained improvement with at least one gamma-aminobutyric acid (GABA) medication, usually diazepam.
Used to help with: Stiff person spectrum disorder.
“Excluding patients with PERM, all patients but 1 had sustained improvements with at least 1 γ-aminobutyric acid agent, usually…”
baclofen
For stiff-person syndrome, oral baclofen can be used as a second-line symptomatic therapy.
Used to help with: Stiff person spectrum disorder.
“The first line of treatment for symptomatic management includes gamma-aminobutyric acid (GABA)ergic agonists, benzodiazepines and baclofen.”
rituximab
Rituximab, a medicine that depletes certain immune cells, has been studied in stiff-person syndrome associated with anti-GAD65 antibodies; a systematic review found it showed efficacy for clinical improvement, though larger controlled trials are still needed.
Used to help with: Stiff person spectrum disorder.
“Rituximab in stiff-person syndrome with glutamic acid decarboxylase 65 autoantibody: a systematic review.”
therapeutic plasma exchange
Therapeutic plasma exchange, which filters antibodies from the blood, may be helpful as an add-on therapy for people with stiff-person syndrome to relieve clinical symptoms, particularly in cases that do not respond to other treatment.
Used to help with: Stiff person spectrum disorder.
“TPE may be helpful as adjuvant therapy for SPS patients to provide relief from clinical symptoms.”
What changes how it shows up
The diagnosis is not the whole story. The factors and open questions below are described in the research mapped here as shaping whether, or how strongly, the condition shows up, or as points the field has not yet settled. They are not, on their own, its cause or its cure.
paraneoplastic origin
Stiff-person syndrome has more than one origin, and which one applies is not settled by the diagnosis alone. Most cases are primary autoimmune (linked to anti-GAD65), while a smaller paraneoplastic subset is driven by an underlying cancer and anti-amphiphysin antibodies. The two are managed differently, so the origin is an open question to work out, not a fixed feature.
Described as modulating: Stiff person spectrum disorder.
“In paraneoplastic SPS, anti-amphiphysin antibodies have been shown in patients with breast cancer or small cell lung cancer.”
paraneoplastic anti-amphiphysin subtype
A paraneoplastic form of stiff-person syndrome, linked to an underlying cancer, is associated with anti-amphiphysin antibodies and has been seen in people with breast cancer or small cell lung cancer.
Described as modulating: Stiff person spectrum disorder.
“In paraneoplastic SPS, anti-amphiphysin antibodies have been shown in patients with breast cancer or small cell lung cancer.”
How to read the evidence labels
Where this comes from
This guide is built from 11 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.
Take it further
Printed, source-linked documents built from this condition's graph — ready to bring to an appointment or attach to a coverage request. Every claim carries its published source, the same as this guide.